1. Field of the Invention
The present invention relates to a stencil printer, an more particularly, to an improvement of means for conducting a leading end of a stencil sheet perforated by stencil sheet perforation means to stencil leading end mounting means of a printing drum.
2. Description of the Prior Art
There has been proposed by Japanese Patent No. 2804695 a stencil printer having stencil sheet leading end holding and transporting means adapted to reciprocate between a vicinity of stencil sheet perforation means and a vicinity of stencil sheet leading end mounting means of a printing drum stopped at a stencil sheet mounting position, wherein the stencil sheet leading end holding and transporting means are operated to hold a leading end of a stencil sheet perforated by the stencil sheet perforation means at an outlet of the stencil sheet perforation means as projecting forward as much as can be clamped by stencil sheet leading end mounting means of the printing drum, and move to the vicinity of the stencil sheet leading end mounting means, and then the printing drum is rotated so as to wind up the stencil sheet therearound, with the stencil sheet leading end holding and transporting means holding the stencil sheet by a force weaker than a stencil sheet holding force of the stencil sheet leading end mounting means of the printing drum, so that thereby the stencil sheet is wound around the printing drum in an expanded condition.
When the stencil sheet leading end holding and transporting means for holding and transporting the stencil sheet leading end from the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum are adapted also to serve as the means for expanding the stencil sheet during a winding-up thereof around the printing drum as in the above-mentioned patent, it is difficult to set up the friction condition of the clamping to be suitable for definitely and stably transporting the leading end of the stencil sheet from the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum and also to be suitable for desirably expanding the stencil sheet without damaging it while it is wound around the printing drum, since these two conditions are not compatible with one another.
Further, when the leading end of the stencil sheet is transported by the stencil sheet leading end holding and transporting means from the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum as projecting forward enough to be caught by the stencil sheet leading end mounting means of the printing drum, when the speed of the transportation increases, the forward projecting leading end of the stencil sheet is bent by a wind caused by the movement thereof, so that the leading end would not be correctly caught by the stencil sheet leading end mounting means of the printing drum.
In consideration of the above-mentioned problems, it is a primary object of the present invention to provide a stencil printer equipped with a stencil sheet leading end guiding carriage improved so as not to cause those problems.
In order to solve, the above-mentioned problems, the present invention proposes a stencil printer comprising:
a printing drum having means provided along a generatrix of a cylindrical circumference thereof for mounting a leading end of a stencil sheet, the printing drum being adapted to be stopped at a predetermined rotational position for mounting the stencil sheet thereon;
means for perforating the stencil sheet; and
a carriage guided to reciprocate between a vicinity of an outlet of the stencil sheet perforation means and a vicinity of the stencil sheet leading end mounting means of the printing drum stopped at the predetermined rotational position;
wherein the carriage has means for selectively clamping the leading end of the stencil sheet perforated by the stencil sheet perforation means, and a pair of rollers for feeding the stencil sheet when the stencil sheet leading end clamping means are not clamping the stencil sheet, the stencil sheet feeding roller pair being adapted to feed the stencil sheet which had been clamped at the leading end thereof by the stencil sheet leading end clamping means toward the stencil sheet leading end mounting means as starting from the leading end when the carriage is positioned in the vicinity of the stencil sheet leading end mounting means of the printing drum stopped at the predetermined rotational position and then to brake the stencil sheet while it is being wound around the circumference of the printing drum with the leading end thereof being held by the stencil sheet leading end mounting means.
By the stencil sheet leading end holding means for holding and pulling the leading end of the stencil sheet from the vicinity of the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum are constructed as means separate from the means for braking the stencil sheet to be expanded while it is being wound around the circumference of the printing drum according to a rotation thereof with the leading end of the stencil sheet being held by the stencil sheet leading end mounting means of the printing drum, the friction condition for ensuring the pulling by clamping of the leading end of the stencil sheet of the stencil sheet leading end clamping means can be determined independently of the friction condition for braking the stencil sheet being wound around the circumference of the printing drum, so that the pulling transportation of the leading end of the stencil sheet from the outlet of the stencil sheet perforation means to the stencil sheet leading end mounting means of the printing drum is definitely ensured, while the stencil sheet can be applied with a desirable expansion when it is wound around the circumference of the printing drum so as not to damage even highly delicately formed perforation images of the stencil sheet.
Further, by the clamping of the leading end of the stencil sheet by the stencil sheet leading end clamping means being released when reached the vicinity of the stencil sheet leading end mounting means of the printing drum, while in turn the leading end of the stencil sheet is fed out forward by the separate stencil sheet feeding roller pair so as to be fed into the stencil sheet leading end mounting means of the printing drum, there occurs no such deformation of the leading end of the stencil sheet as by a running wind during the transportation thereof from the outlet of the stencil sheet perforation means to the vicinity of the stencil sheet leading end mounting means of the printing drum even when the speed of the transportation is increased. Further, by such an arrangement that the leading end of the stencil sheet is fed into the stencil sheet leading end mounting means of the printing drum by the stencil sheet leading end feeding roller pair in the vicinity thereof with a control of the stencil sheet leading end feeding roller pair for a very small distance of transportation independently of a control of transportation for a relatively large distance of transportation extended from the outlet of the stencil sheet perforation means to the stencil sheet leading end mounting means of the printing drum, the means for each of the two separate controls can be individually optimized with respect to the strength and the sensitivity of their constructions, so that the leading end of the stencil sheet is always mounted to the stencil sheet leading end mounting means of the printing drum in a predetermined correct mounting condition.
In more detail, the carriage may have a main frame, and an auxiliary frame pivotably supported by the main frame, the stencil sheet leading end clamping means having a lower clamping element and an upper clamping element, the stencil sheet feeding roller pair having a lower roller and an upper roller, the lower clamping element and the lower roller being mounted on the main frame, the upper clamping element and the upper roller being mounted on the auxiliary frame, the auxiliary frame being adapted to be pivoted relative to the main frame by an action of a cam follower engaging a cam when the carriage comes to the vicinity of the outlet of the stencil sheet perforation means so as to remove the upper clamping element and the upper roller from the lower damping element and the lower roller, respectively.
In such a construction, the auxiliary frame may be biased toward a regular position relative to the main frame by a spring.
The stencil printer of the above construction may further comprise a pair of guide rails extending between the vicinity of the outlet of the stencil sheet perforation means and the vicinity of the stencil sheet leading end mounting means of the printing drum stopped at the predetermined rotational position, the carriage being supported and guided by the guide rail pair at opposite side portions thereof.
In such a construction, the guide rails may have a branch portion adapted to be selectively branched in a way thereof, the carriage being capable of supplying the stencil sheet to at least two printing drums separately according to a non-branched state and a branched state.
Further, the guide rail pair may be deflected at an end portion thereof close to the stencil sheet perforation means so that the carriage coming to the vicinity of the outlet of the stencil sheet perforation means is inclined so as to bias an end of the main frame thereof close to the stencil sheet perforation means downward relative to the stencil sheet perforation means, so that thereby the lower clamping element and the lower roller are biased downward relative to the outlet of the stencil sheet perforation means, while the upper clamping element and the upper roller are biased upward relative to the outlet of the stencil sheet perforation means.